This section contains a number of benchmarks from a real-world system
using software RAID. There is some general information about benchmarking
software too.

Benchmark samples were done with the bonnie program, and at all
times on files twice- or more the size of the physical RAM in the machine.

The benchmarks here only measures input and output bandwidth
on one large single file. This is a nice thing to know, if it's
maximum I/O throughput for large reads/writes one is interested in.
However, such numbers tell us little about what the performance would
be if the array was used for a news spool, a web-server, etc. etc.
Always keep in mind, that benchmarks numbers are the result of running
a "synthetic" program. Few real-world programs do what
bonnie does, and although these I/O numbers are nice to look
at, they are not ultimate real-world-appliance performance
indicators. Not even close.

For now, I only have results from my own machine. The setup is:

Dual Pentium Pro 150 MHz

256 MB RAM (60 MHz EDO)

Three IBM UltraStar 9ES 4.5 GB, SCSI U2W

Adaptec 2940U2W

One IBM UltraStar 9ES 4.5 GB, SCSI UW

Adaptec 2940 UW

Kernel 2.2.7 with RAID patches

The three U2W disks hang off the U2W controller, and the UW disk off
the UW controller.

It seems to be impossible to push much more than 30 MB/s thru the SCSI
busses on this system, using RAID or not. My guess is, that because
the system is fairly old, the memory bandwidth sucks, and thus limits
what can be sent thru the SCSI controllers.

Read is Sequential block input, and Write
is Sequential block output. File size was 1GB in all
tests. The tests where done in single-user mode. The SCSI driver was
configured not to use tagged command queuing.

Chunk size

Block size

Read kB/s

Write kB/s

4k

1k

19712

18035

4k

4k

34048

27061

8k

1k

19301

18091

8k

4k

33920

27118

16k

1k

19330

18179

16k

2k

28161

23682

16k

4k

33990

27229

32k

1k

19251

18194

32k

4k

34071

26976

>From this it seems that the RAID chunk-size doesn't make that much
of a difference. However, the ext2fs block-size should be as large as
possible, which is 4kB (eg. the page size) on IA-32.

RAID-10 is "mirrored stripes", or, a RAID-1 array of two RAID-0
arrays. The chunk-size is the chunk sizes of both the RAID-1 array and
the two RAID-0 arrays. I did not do test where those chunk-sizes
differ, although that should be a perfectly valid setup.

Chunk size

Block size

Read kB/s

Write kB/s

32k

1k

13753

11580

32k

4k

23432

22249

No more tests where done. The file size was 900MB, because the four
partitions involved where 500 MB each, which doesn't give room for a
1G file in this setup (RAID-1 on two 1000MB arrays).

To check out speed and performance of your RAID systems, do NOT use hdparm.
It won't do real benchmarking of the arrays.

Instead of hdparm, take a look at the tools described here: IOzone and Bonnie++.

IOzone is a small, versatile
and modern tool to use. It benchmarks file I/O performance for read, write, re-read, re-write, read backwards, read strided, fread, fwrite, random read, pread, mmap, aio_read and aio_write operations.
Don't worry, it can run on any of the ext2, ext3, reiserfs, JFS, or XFS
filesystems in OSDL STP.

You can also use IOzone to show throughput performance as a function of
number of processes and number of disks used in a filesystem, something
interesting when it's about RAID striping.

Although documentation for IOzone is available in Acrobat/PDF, PostScript, nroff,
and MS Word formats, we are going to cover here a nice example of IOzone in action:

Now you just need to know about the feature that makes IOzone useful for RAID
benchmarking: the file operations involving RAID are the read strided.
The example above shows a 380.952Kb/sec. for the read strided, so you
can go figure.

Bonnie++ seems to be more targeted at benchmarking single drives that
at RAID, but it can test more than 2Gb of storage on 32-bit machines, and tests
for file creat, stat, unlink operations.